The basic function of a monopulse radar system is to determine the direction of a target with respect to the radar antenna from a single pulse of electromagnetic energy received by the antenna from the target. This is generally accomplished by utilizing an antenna array which comprises several individual elements which are arranged in a regular pattern. The signals received by each antenna are slightly different, so a comparison of the several signals results in the needed direction information.
The use of four-port hybrid junctions as elements of monopulse comparator circuits is well known. Comparator circuits of this type are commonly manufactured in microstrip for use at microwave frequencies. However, the adaptation to higher, millimeter wave frequencies challenges the capability of known microstrip technology to produce accurate, repeatable and inexpensive comparator circuits. These problems are enhanced if it is desired to obtain a comparator circuit of the smallest possible overall dimensions. Particular problems encountered are the use of relatively expensive ceramic substrates, the lack of an efficient circuit layout to reduce overall dimensions and electromagnetic coupling between closely spaced microstrip lines.